A 24 year old man presents with multiple small hypopigmented patches around hair follicles on upper chest and back. These macules were with fine scaling which coalesced later. He had received treatment 1 year back for the same type of lesion. Which of the following investigation should be done to diagnose this condition?

The characteristic lesion seen in this patient is typical of tinea versicolor caused by a nondermatophyte, dimorphic fungus, Malassezia furfur. It is diagnosed by making a KOH preparation from scaling lesions which demonstrate a confluence of sho hyphae and round spores known as "spaghetti and meatballs" appearance. The typical lesion of tinea versicolor consists of oval scaly macules, papules, and patches concentrated on the chest, shoulders, and back, and rarely on the face or distal extremities. In patients with dark skin they are seen as hypopigmented areas, while on light skin, they are slightly erythematous or hyperpigmented. Ref: McCall C.O. (2012). Chapter 52. Eczema, Psoriasis, Cutaneous Infections, Acne, and Other Common Skin Disorders. In D.L. Longo, A.S. Fauci, D.L. Kasper, S.L. Hauser, J.L. Jameson, J. Loscalzo (Eds),Harrison's Principles of Internal Medicine, 18e.